Plating method

ABSTRACT

An object of the present invention is to provide a plating method which can form defect-free, completely-embedded interconnects of a conductive material in recesses in the surface of a substrate even when the recesses are of a high aspect ratio, and which can improve the flatness of a plated film on the substrate even when narrow trenches and broad trenches are co-present in the surface of the substrate. A plating method according to the present invention includes: providing a high resistance structure between a surface of a substrate, said surface being connected to a cathode electrode, and an anode electrode; filling the space between the substrate and the anode electrode with a plating solution while applying a voltage between the cathode electrode and the anode electrode; and growing a plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at a constant value.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a plating method, and more particularly to a plating method for filling a conductive metal such as copper (Cu) or the like in fine interconnection patterns (recesses) formed in a substrate such as a semiconductor wafer to form interconnects.

[0003] 2. Description of the Related Art

[0004] In recent years, instead of using aluminum or aluminum alloys as a material for forming interconnection circuits on a semiconductor substrate, there is an eminent movement towards using copper (Cu) that has a low electric resistivity and high electromigration endurance. Copper interconnects are generally formed by filling copper into fine recesses formed in the surface of a substrate. Various techniques for forming such copper interconnects are known, including CVD, sputtering, and plating. According to any such techniques, a copper film is formed in the substantially entire surface of a substrate, followed by removal of unnecessary copper by performing chemical mechanical polishing (CMP).

[0005]FIGS. 21A through 21C illustrate, in sequence of basic process steps, an example for producing a semiconductor device having copper interconnects by performing copper plating onto a surface of a substrate. As shown in FIG. 21A, an insulating film 2, such as a silicon oxide film of SiO₂ or a film of low-k material, is deposited on a conductive layer 1 a in which electronic devices are formed, which is formed on a semiconductor base 1. Fine recesses 5 composed of contact holes 3 and trenches 4 for interconnects are formed in the insulating film 2 by a lithography/etching technique. A barrier layer 6 of TaN or the like is formed on the entire surface of the insulating film 2.

[0006] Then, as shown in FIG. 21B, copper plating is performed onto a surface of the semiconductor substrate W to fill the recesses (holes) 5 of the semiconductor substrate W with copper and, at the same time, deposit a copper film 7 on the barrier layer 6. Thereafter, the copper film 7 and the barrier layer 6 on the insulating film 2 are removed by performing chemical mechanical polishing (CMP) so as to make the surface of the copper filled in the contact holes 3 and the trenches 4 for interconnects and the surface of the insulating film 2 lie substantially on the same plane. Embedded interconnects composed of the copper film 7, as shown in FIG. 21C, are thus formed.

[0007] In the embedding of copper film 7 e.g. by an electroplating method in the fine recesses 5 provided in the surface of the semiconductor substrate W, it is widely practiced, in advance of the copper plating, to form a seed layer 8 e.g. by sputtering or CVD on the surface of the barrier layer 6 formed in the surface of the semiconductor substrate W, as shown in FIG. 22. The main objective of the seed layer 8 is to make the surface of the seed layer 8 serve as an electrical cathode to supply a sufficient electrical current for reducing metal ions in a plating solution and depositing the metal ions as a solid metal.

[0008] The seed layer 8 is formed usually by sputtering, CVD or the like. As interconnects are now becoming highly densified and finer, the aspect ratios of contact holes and via holes are becoming higher. For example, as shown in FIG. 22, when a seed layer 8 e.g. of copper is formed over a recess (hole) 5 having a diameter of about 0.15 μm and an aspect ratio of about 6, the ratio B₁/A₁(side coverage), i.e. the ratio of the film thickness B₁ of the seed layer 8 on the internal side surface of the recess 5 to the film thickness A₁ of the seed layer 8 on the external surface of the substrate W, is about 5 to 10%. Further, in this case, it is difficult to form a continuous seed layer 8. This is considered to be partly due to cohesion of sputtered copper atoms upon film formation. In addition, there is a current tendency that the film thickness A₁ of the seed layer 8 on the external substrate surface is becoming as thin as no more than 80-100 nm, particularly even no more than 40-60 nm, and accordingly, the film thickness B₁ of the seed layer 8 on the internal side surface of the recess 5 is also becoming thinner.

[0009] A plating solution, in general, is composed of copper sulfate, sulfuric acid, chlorine and several types of additives, and is strongly acidic. Thus, a plating solution has the nature of dissolving the seed layer 8 of copper. Accordingly, as shown in FIG. 23, in carrying out electroplating of the substrate W, having on its surface the above-described seed layer 8, to form copper interconnects, the seed layer 8 can be dissolved by the plating solution upon contact of the substrate W with the plating solution. In particular, the seed layer 8 can be dissolved out in the sidewalls of fine holes or trenches, especially at portions near the bottoms of the holes or trenches, resulting in electrical non-conductivity and formation of voids at those portions.

[0010] If the film thickness A₁ of the seed layer 8 on the external substrate surface, shown in FIG. 22, is made large for the purpose of ensuring the side coverage, the substantial aspect ratio of the recess 5 should then be increased. Further, blockage of the opening of the hole could occur upon embedding of copper, whereby a void will be formed in the hole, leading to a decreased yield.

[0011] On the other hand, when a barrier layer 6 is formed on the surface of a substrate W in which relatively small and large fine recesses, e.g. narrow trenches 5 a and broad trenches 5 b, are co-present in the surface, as shown in FIG. 24A, and a seed layer 8 is formed on the barrier layer 6, as shown in FIG. 24B, and then copper is embedded in the trenches 5 a, 5 b by copper plating, as shown in FIG. 24C, the growth of plating tends to be promoted over the narrow trenches 5 a, whereby the plated copper film 7 is likely to be raised even when the plating solution or an additive in the plating solution is optimized, whereas plating with a sufficiently high leveling cannot be effected in the broad trenches 5 b, resulting in an insufficient embedding of copper.

[0012] In this regard, it may be considered to increase the overall thickness of embedded copper film in order to prevent the insufficient embedding. When considering a later CMP processing for flattening the surface of the substrate W, however, a thicker plated film necessarily increases the polishing amount, thus necessarily prolonging the processing time. Increasing a CMP rate to avoid the processing time prolongation could cause dishing in the broad trenches 5 b during the CMP processing.

[0013] In order to solve these problems, it is necessary to make the thickness of a plated film as thin as possible, and reduce or eliminate the raised portions and recesses in the plated film even when narrow trenches and broad trenches are co-present in the surface of a substrate to thereby improve the flatness of the plated film. At present, however, when performing plating using, for example, a copper sulfate plating bath, it is not possible to simultaneously decrease the raised portions and decrease the recesses solely by the action of the plating solution or an additive.

SUMMARY OF THE INVENTION

[0014] The present invention has been made in view of the above situation in the related art. It is therefore an object of the present invention to provide a plating method which can form defect-free, completely-embedded interconnects of a conductive material in recesses in the surface of a substrate even when the recesses are of a high aspect ratio, and which can improve the flatness of a plated film on the substrate even when narrow trenches and broad trenches are co-present in the surface of the substrate, enabling a later CMP processing to be carried out in a short time while preventing dishing during the CMP processing.

[0015] In order to achieve the above object, the present invention provides a plating method, comprising: providing a high resistance structure between a surface of a substrate, said surface being connected to a cathode electrode, and an anode electrode; filling the space between the substrate and the anode electrode with a plating solution while applying a voltage between the cathode electrode and the anode electrode; and growing a plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at a constant value.

[0016] This method can prevent a seed layer from being dissolved by a plating solution that is supplied onto the surface of a substrate to perform plating, and can therefore enable a plated film to grow on the seed layer to effect embedding of e.g. copper.

[0017] In a preferred embodiment of the present invention, the voltage applied is such as to allow an electric current with an average cathodic current density, with respect to the surface of the substrate, of 1 to 30 mA/cm² to flow.

[0018] The voltage is preferably applied for 100 to 2000 msec after the electric current begins to flow between the cathode electrode and the anode electrode.

[0019] The present invention provides another plating method, comprising: providing a high resistance structure between a surface of a substrate, said surface being connected to a cathode electrode, and an anode electrode; filling the space between the substrate and the anode electrode with a plating solution; and growing a plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at stepwise changing constant values.

[0020] It becomes possible with this plating method to carry out a first-step plating at a low electric current to reinforce a seed layer on a substrate and carry out a second-step plating to grow a plated film on the seed layer to effect embedding of e.g. copper. Such a stepwise plating makes it possible to form defect-free, completely-embedded interconnects of a conductive material, such as copper, in recesses in the surface of a substrate even when the recesses are of a high aspect ratio.

[0021] In a preferred embodiment of the present invention, the value of the electric current flowing between the cathode electrode and the anode electrode is increased stepwise.

[0022] In a preferred embodiment of the present invention, the plating solution is changed for a different plating solution in the process of film formation.

[0023] In a preferred embodiment of the present invention, the surface of the substrate is cleaned in the process of film formation.

[0024] The present invention also provides yet another plating method, comprising: providing a high resistance structure between a surface of a substrate, said surface being connected to a cathode electrode, and a anode electrode; filling the space between the substrate and the anode electrode with a plating solution; growing a plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at a constant value; reversing the direction of the electric current flowing between the cathode electrode and the anode electrode to etch away the surface of the plated film; and further growing the plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at a constant value.

[0025] According to this method, the surface of a plated film is etched away between plating processings to flatten the plated film, whereby the flatness of the final plated film can be improved.

[0026] In a preferred embodiment of the present invention, the step of etching the surface of the plated film and the subsequent step of growing the plated film are carried out repeatedly.

[0027] The present invention also provides yet another plating method, comprising: filling the space between a surface of a substrate, said surface being connected to a cathode electrode, and an anode electrode with a plating solution while applying a voltage between the cathode electrode and the anode electrode; and growing a plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at a constant value.

[0028] The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings that illustrates preferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is an overall plan view of a substrate processing apparatus provided with a plating apparatus for carrying out a plating method according to the present invention;

[0030]FIG. 2 is a plan view of the plating apparatus shown in FIG. 1;

[0031]FIG. 3 is an enlarged sectional view of the substrate holder and the electrode portion of the plating apparatus shown in FIG. 1;

[0032]FIG. 4 is a front view of the pre-coating/recovering arm of the plating apparatus shown in FIG. 1;

[0033]FIG. 5 is a plan view of the substrate holder of the plating apparatus shown in FIG. 1;

[0034]FIG. 6 is a cross-sectional view taken along the line B-B of FIG. 5;

[0035]FIG. 7 is a cross-sectional view taken along the line C—C of FIG. 5;

[0036]FIG. 8 is a plan view of the electrode portion of the plating apparatus shown in FIG. 1;

[0037]FIG. 9 is a cross-sectional view taken along the line D-D of FIG. 8;

[0038]FIG. 10 is a plan view of the electrode arm section of the plating apparatus shown in FIG. 1;

[0039]FIG. 11 is a schematic sectional view illustrating the electrode head and the substrate holder of the plating apparatus shown in FIG. 1 upon electroplating;

[0040]FIG. 12 is a graph showing the relationship between electric current and time in a control method (plating method) as carried out by the plating apparatus shown in FIG. 1;

[0041]FIG. 13 is a graph showing the relationship between electric current and time in another control method (plating method) as carried out by the plating apparatus shown in FIG. 1;

[0042]FIG. 14 is a graph showing the relationship between electric current and time in yet another control method (plating method) as carried out by the plating apparatus shown in FIG. 1;

[0043]FIG. 15 is a graph showing the relationship between electric current and time in yet another control method (plating method) as carried out by the plating apparatus shown in FIG. 1;

[0044]FIG. 16 is a graph showing the relationship between electric current and time in yet another control method (plating method) as carried out by the plating apparatus shown in FIG. 1;

[0045]FIGS. 17A through 17C are diagrams illustrating a series of a first-step plating, an intermediate etching step and a second-step plating, the etching step being carried out by applying a reverse current;

[0046]FIG. 18 is a schematic diagram illustrating another plating apparatus;

[0047]FIG. 19 is an overall plan view of another substrate processing apparatus provided with a plating apparatus useful for carrying out a plating method according to the present invention;

[0048]FIG. 20 is a block diagram illustrating a substrate processing process as carried out by the substrate processing apparatus shown in FIG. 19;

[0049]FIGS. 21A through 21C are diagrams illustrating, in a sequence of process steps, an example of the formation of copper interconnects by plating;

[0050]FIG. 22 is a diagram illustrating the formation of a seed layer on the surface of a recess (hole) having a high aspect ratio;

[0051]FIG. 23 is a diagram illustrating the problem of dissolution of the seed layer shown in FIG. 22 upon its contact with a plating solution; and

[0052]FIGS. 24A through 24C are diagrams illustrating the formation of embedded interconnects by copper plating of a substrate as carried out by a conventional method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] Preferred embodiments of the present invention will now be described in detail with reference to the drawings. The following embodiments relate to the application of the present invention useful for forming interconnects of copper by embedding copper in fine recess for interconnects formed in a surface of the substrate.

[0054]FIG. 1 is a plan view showing a substrate processing apparatus incorporating a plating apparatus for performing a plating method according to the present invention. As shown in FIG. 1, this substrate processing apparatus has a rectangular facility which houses therein two loading/unloading units 10 for housing a plurality of substrates W therein, two plating apparatuses 12 for performing plating process, a transfer robot 14 for transferring substrates W between the loading/unloading units 10 and the plating apparatuses 12, and plating solution supply equipment 18 having a plating solution tank 16.

[0055] The plating apparatus 12, as shown in FIG. 2, is provided with a substrate processing section 20 for performing plating process and processing incidental thereto, and a plating solution tray 22 for storing a plating solution is disposed adjacent to the substrate processing section 20. There is also provided an electrode arm portion 30 having an electrode head 28 which is held at the front end of an arm 26 swingable about a rotating shaft 24 and which is swung between the substrate processing section 20 and the plating solution tray 22. Furthermore, a pre-coating/recovering arm 32, and fixed nozzles 34 for ejecting pure water or a chemical liquid such as ion water, and further a gas or the like toward a substrate are disposed laterally of the substrate processing section 20. In this embodiment, three of the fixed nozzles 34 are disposed, and one of them is used for supplying pure water.

[0056] The substrate processing section 20, as shown in FIG. 3, has a substrate holder 36 for holding a substrate W with its surface (plating surface) facing upward, and a electrode portion 38 located above the substrate holder 36 so as to surround a peripheral portion of the substrate holder 36. Further, a substantially cylindrical bottomed cup 40 surrounding the periphery of the substrate holder 36 for preventing scatter of various chemical liquids used during processing is provided so as to be vertically movable by an air cylinder (not shown).

[0057] The substrate holder 36 is adapted to be raised and lowered by the air cylinder 44 between a lower substrate transfer position A, an upper plating position B, and a pretreatment/cleaning position C intermediate between these positions. The substrate holder 36 is also adapted to rotate at an arbitrary acceleration and an arbitrary velocity integrally with the electrode portion 38 by a rotating motor and a belt (not shown). Substrate carry-in and carry-out openings (not shown) are provided in confrontation with the substrate transfer position A in a side panel of the plating apparatus 12 facing the transfer robot 14. When the substrate holder 36 is raised to the plating position B, a sealing member 90 and cathode electrodes 88 (to be described below) of the electrode portion 38 are brought into contact with the peripheral edge portion of the substrate W held by the substrate holder 36. On the other hand, the cup 40 has an upper end located below the substrate carry-in and carry-out openings, and when the cup 40 ascends, the upper end of the cup 40 reaches a position above the electrode portion 38 closing the substrate carry-in and carry-out openings, as shown by imaginary lines in FIG. 3.

[0058] The plating solution tray 22 serves to wet a high resistance structure 110 and an anode electrode 98 (to be described later on) of the electrode arm portion 30 with a plating solution, when plating has not been performed. The plating solution tray 22 is set at a size in which the high resistance structure 110 can be accommodated, and the plating solution tray 22 has a plating solution supply port and a plating solution drainage port (not shown). A photo-sensor is attached to the plating solution tray 22, and can detect brimming with the plating solution in the plating solution tray 22, i.e., overflow, and drainage.

[0059] The electrode arm portion 30 is vertically movable by a vertical movement motor 132, which is a servomotor, and a ball screw 134, and swingable between the plating solution tray 22 and the substrate processing section 20 by a swing motor, in this embodiment, as described bellow. A compressed actuator may be used.

[0060] As shown in FIG. 4, the pre-coating/recovering arm 32 is coupled to an upper end of a vertical support shaft 58. The pre-coating/recovering arm 32 is swingable by a rotary actuator 60 and is also vertically moveable by an air cylinder (not shown). The pre-coating/recovering arm 32 supports a pre-coating nozzle 64 for discharging a pre-coating liquid, on its free end side, and a plating solution recovering nozzle 66 for recovering the plating solution, on a portion closer to its proximal end. The pre-coating nozzle 64 is connected to a syringe that is actuatable by an air cylinder, for example, for intermittently discharging a pre-coating liquid from the pre-coating nozzle 64. The plating solution recovering nozzle 66 is connected to a cylinder pump or an aspirator, for example, to draw the plating solution on the substrate from the plating solution recovering nozzle 66.

[0061] As shown in FIGS. 5 through 7, the substrate holder 36 has a disk-shaped substrate stage 68 and six vertical support arms 70 disposed at spaced intervals on the circumferential edge of the substrate stage 68 for holding a substrate W in a horizontal plane on respective upper surfaces of the support arms 70. A positioning plate 72 is mounted on an upper end one of the support arms 70 for positioning the substrate by contacting the end face of the substrate. A pressing finger 74 is rotatably mounted on an upper end of the support arm 70, which is positioned opposite to the support arm 70 having the positioning plate 72, for abutting against an end face of the substrate W and pressing the substrate W to the positioning plate 72 when rotated. Chucking fingers 76 are rotatably mounted on upper ends of the remaining four support arms 70 for pressing the substrate W downwardly and gripping the circumferential edge of the substrate W.

[0062] The pressing finger 74 and the chucking fingers 76 have respective lower ends coupled to upper ends of pressing pins 80 that are normally urged to move downwardly by coil springs 78. When the pressing pins 80 are moved downwardly, the pressing finger 74 and the chucking fingers 76 are rotated radially inwardly into a closed position. A support plate 82 is disposed below the substrate stage 68 for engaging lower ends of the opening pins 80 and pushing them upwardly.

[0063] When the substrate holder 36 is located in the substrate transfer position A shown in FIG. 3, the pressing pins 80 are engaged and pushed upwardly by the support plate 82, so that the pressing finger 74 and the chucking fingers 76 rotate outwardly and open. When the substrate stage 68 is elevated, the opening pins 80 are lowered under the resiliency of the coil springs 78, so that the pressing finger 74 and the chucking fingers 76 rotate inwardly and close.

[0064] As shown in FIGS. 8 and 9, the electrode portion 38 comprises an annular frame 86 fixed to upper ends of vertical support columns 84 mounted on the peripheral edge of the support plate 82 (see FIG. 7), a plurality of, six in this embodiment, cathode electrodes 88 attached to a lower surface of the annular frame 86 and projecting inwardly, and an annular sealing member 90 mounted on an upper surface of the annular frame 86 in covering relation to upper surfaces of the cathode electrodes 88. The sealing member 90 is adapted to have an inner peripheral edge portion inclined inwardly downwardly and progressively thin-walled, and to have an inner peripheral end suspending downwardly.

[0065] When the substrate holder 36 has ascended to the plating position B, as shown FIG. 3, the cathode electrodes 88 are pressed against the peripheral edge portion of the substrate W held by the substrate holder 36 for thereby allowing electric current to pass through the substrate W. At the same time, an inner peripheral end portion of the sealing member 90 is brought into contact with an upper surface of the peripheral edge of the substrate W under pressure to seal its contact portion in a watertight manner. As a result, the plating solution supplied onto the upper surface (plating surface) of the substrate W is prevented from seeping from the end portion of the substrate W, and the plating solution is prevented from contaminating the cathode electrodes 88.

[0066] In the present embodiment, the electrode portion 38 is vertically immovable, but rotatable in a body with the substrate holder 36. However, the electrode portion 38 may be arranged such that it is vertically movable and the sealing member 90 is pressed against the surface, to be plated, of the substrate W when the electrode portion 38 is lowered.

[0067] As shown in FIGS. 10 and 11, the electrode head 28 of the electrode arm section 30 includes a housing 94 which is coupled via a ball bearing 92 to the free end of the pivot arm 26, and a high resistance structure 110 which is disposed such that it closes the bottom opening of the housing 94. The housing 94 has at its lower end an inwardly-projecting portion 94 a, while the high resistance structure 110 has at its top a flange portion 110 a. The flange portion 110 a is engaged with the inwardly-projecting portion 94 a and a spacer 96 is interposed therebetween. The high resistance structure 110 is thus held with the housing 94, while a hollow plating solution chamber 100 is defined in the housing 94.

[0068] The high resistance structure 110 is composed of porous ceramics such as alumina, SiC, mullite, zirconia, titania or cordierite, or a hard porous material such as a sintered compact of polypropylene or polyethylene, or a composite material comprising these materials. In case of the alumina-based ceramics, for example, the ceramics with a pore diameter of 30 to 200 μm is used. In case of the SiC, SiC with a pore diameter of not more than 30 μm, a porosity of 20 to 95%, and a thickness of about 1 to 20 mm, preferably 5 to 20 mm, more preferably 8 to 15 mm, is used. The high resistance structure 110, in this embodiment, is constituted of porous ceramics of alumina having a porosity of 30%, and an average pore diameter of 100 μm. The porous ceramic plate per se is an insulator, but the high resistance structure is constituted by causing the plating solution to enter its interior complicatedly and follow a considerably long path in the thickness direction.

[0069] The high resistance structure 110, which has the high resistance, is disposed in the plating solution chamber 100. Hence, the influence of the resistance of the seed layer 8 (see FIG. 22) becomes a negligible degree. Consequently, the difference in current density over the surface of the substrate due to electrical resistance on the surface of the substrate W becomes small, and the uniformity of the plated film over the surface of the substrate improves.

[0070] In the plating solution chamber 100, there is disposed an anode electrode 98 held in abutment against an lower surface of a plating solution introduction pipe 104 disposed above the anode electrode 98. The plating solution introduction pipe 104 has a plating solution introduction port 104 a connected to a plating solution supply pipe 102 which extends from the plating solution supply unit 18 (see FIG. 1). A plating solution discharge port 94 b provided in an upper plate of the housing 94 is connected to an plating solution discharge pipe 106 communicating with the plating solution chamber 100.

[0071] A manifold structure is employed for the plating solution introduction pipe 104 so that the plating solution can be supplied uniformly onto the plating surface of the substrate. In particular, a large number of narrow tubes 112, communicating with the plating solution introduction pipe 104, are connected to the pipe 104 at predetermined positions along the long direction of the pipe 104. Further, small holes are provided in the anode electrode 98 and the high resistance structure 110 at positions corresponding to the narrow tubes 112. The narrow tubes 112 extend downwardly in the small holes and reach the lower surface or its vicinity of the high resistance structure 110.

[0072] Thus, the plating solution, introduced from the plating solution supply pipe 102 into the plating solution introduction pipe 104, passes through the narrow tubes 112 and reaches the bottom of the high resistance structure 110, and pass through the high resistance structure 110 and fills the plating solution chamber 100, whereby the anode electrode 98 is immersed in the plating solution. The plating solution is discharged from the plating solution discharge pipe 106 by application of suction to the plating solution discharge pipe 106.

[0073] In order to suppress slime formation, the anode electrode 98 is made of copper (phosphorus-containing copper) containing 0.03 to 0.05% of phosphorus. It is also possible to use an insoluble material for the anode electrode 98.

[0074] The cathode electrodes 88 are electrically connected to the negative pole of a plating power source 114, and the anode electrode 98 is electrically connected to the positive pole of the plating power source 114. The plating power source 114 can change the direction of current flow alternatively.

[0075] The ball bearing 92 is coupled to the pivot arm 26 via a support member 124. The pivot arm 26 is vertically movable by a vertical movement motor 132, which is a servomotor, and a ball screw 134. It is also possible to use a compressed air actuator to constitute a vertical movement mechanism.

[0076] When carrying out electroplating, the substrate holder 36 is positioned at the plating position B (see FIG. 3). As shown in FIG. 11, the electrode head 28 is lowered until the distance between the substrate W held by the substrate holder 36 and the high resistance structure 110 becomes e.g. about 0.1 to 3 mm. A plating solution is supplied from the plating solution supply pipe 102 to the upper surface (plating surface) of the substrate W while impregnating the high resistance structure 110 with the plating solution and filling the plating solution chamber 100 with the plating solution to carry out plating of the plating surface of the substrate W.

[0077] The operation of the substrate processing apparatus incorporating the above-described plating apparatus will now be described by furthermore referring to FIG. 12.

[0078] First, a substrate W to be plated is taken out from one of the loading/unloading units 10 by the transfer robot 14, and transferred, with the surface to be plated facing upward, through the substrate carry-in and carry-out opening defined in the side panel, into one of the plating apparatuses 12. At this time, the substrate holder 36 is in the lower substrate transfer position A. After the hand of the transfer robot 14 has reached a position directly above the substrate stage 68, the hand of the transfer robot 14 is lowered to place the substrate W on the support arms 70. The hand of the transfer robot 14 is then retracted through the substrate carry-in and carry-out opening.

[0079] After the hand of the transfer robot 14 is retracted, the cup 40 is elevated. Then, the substrate holder 36 is lifted from the substrate transfer position A to the pretreatment/cleaning position C. As the substrate holder 36 ascends, the substrate W placed on the support arms 70 is positioned by the positioning plate 72 and the pressing finger 74, and then reliably gripped by the chucking fingers 76.

[0080] On the other hand, the electrode head 28 of the electrode arm portion 30 is in a normal position over the plating solution tray 22 now, and the high resistance structure 110 or the anode electrode 98 is positioned in the plating solution tray 22. At the same time that the cup 40 ascends, the plating solution starts being supplied to the plating solution tray 22 and the electrode head 28. Until the step of plating the substrate W is initiated, the new plating solution is supplied, and the plating solution discharge pipe 106 is evacuated to replace the plating solution in the high resistance structure 110 and remove air bubbles from the plating solution in the high resistance structure 110. When the ascending movement of the cup 40 is completed, the substrate carry-in and carry-out opening in the side panel is closed by the cup 40, isolating the atmosphere in the side panel and the atmosphere outside of the side panel from each other.

[0081] When the cup 40 is elevated, the pre-coating step is initiated. Specifically, the substrate holder 36 that has received the substrate W is rotated, and the pre-coating/recovering arm 32 is moved from the retracted position to a position confronting the substrate W. When the rotational speed of the substrate holder 36 reaches a preset value, the pre-coating nozzle 64 mounted on the tip end of the pre-coating/recovering arm 32 intermittently discharges a pre-coating liquid which comprises a surface active agent, for example, toward the plating surface of the substrate W. At this time, since the substrate holder 36 is rotating, the pre-coating liquid spreads all over the plating surface of the substrate W. Then, the pre-coating/recovering arm 32 is returned to the retracted position, and the rotational speed of the substrate holder 36 is increased to spin the pre-coating liquid off and dry the plating surface of the substrate W.

[0082] After the completion of the pre-coating step, the plating step is initiated. First, the substrate holder 36 is stopped against rotation, or the rotational speed thereof is reduced to a preset rotational speed for plating. In this state, the substrate holder 36 is lifted to the plating position B. Then, the peripheral edge of the substrate W is brought into contact with the cathode electrodes 88, when it is possible to pass an electric current, and at the same time, the sealing member 90 is pressed against the upper surface of the peripheral edge of the substrate W, thus sealing the peripheral edge of the substrate W in a watertight fashion.

[0083] Based on a signal indicating that the pre-coating step for the loaded substrate W is completed, the electrode arm portion 30 is swung in a horizontal direction to displace the electrode head 28 from a position over the plating solution tray 22 to a position over the plating processing position. After the electrode head 28 reaches this position, the electrode head 28 is lowered toward the electrode portion 38. At this time, the high resistance structure 110 does not contact with the plating surface of the substrate W, but is held closely to the plating surface of the substrate W at a distance ranging from 0.1 mm to 3 mm. When the descent of the electrode head 28 is completed, the plating process is initiated.

[0084] In particular, as shown in FIG. 12, the negative pole of the plating power source 114 is connected to the cathode electrodes 88 and the positive pole is connected to the anode electrode 98, and a constant voltage is applied between the cathode electrodes 88 and the anode electrode 98, i.e. constant voltage control is carried out, while a plating solution is supplied from the plating solution supply pipe 102 into the electrode head 28, so that the plating solution is supplied onto the upper surface (plating surface) of the substrate W while the high resistance structure 110 is impregnated with the plating solution and the plating solution chamber 100 is filled with the plating solution (t₀-t₁). The voltage is preferably such as to allow an electric current with an average cathodic current density, with respect to the surface of the substrate W, of 1 mA/cm² to 30 mA/cm² to flow. The time period for applying the voltage is generally 100 to 2000 msec, preferably 300 to 1000 msec from the moment at which the electric current begins to flow between the cathode electrodes 88 and the anode electrode 98.

[0085] According to this embodiment, the moment at which the electric current begins to flow between the cathode electrodes 88 and the anode electrode 98 is deemed as a liquid-contact point. However, it is also possible, for example, to allow a weak direct current or alternating current to flow between the cathode electrodes 88 and the anode electrode 98 in advance, and determine a liquid-contact point by detecting a change in voltage.

[0086] By thus supplying the plating solution while carrying out a constant voltage control, i.e. applying a constant voltage between the cathode electrodes 88 and the anode electrode 98, the drawback of dissolution of seed layer 8 in the prior art as illustrated in FIG. 23 can be overcome. Thus, according to a conventional plating method, as shown in FIG. 23, a seed layer 8 on a substrate W can be dissolved by a plating solution upon contact of the substrate W with the plating solution. In particular, the seed layer 8 can be dissolved out in the sidewalls of fine holes or trenches, especially at portions near the bottoms of the holes or trenches, resulting in non-conductivity at those portions. Such a drawback can be overcome by the present method, and plating can be initiated in such a state that a seed layer 8 is present over the entire surfaces of recesses 5, as shown in FIG. 22.

[0087] After completion of the filling of plating solution, a plated film is allowed to grow on the surface (seed layer 8) of the substrate while carrying out constant current control, i.e., applying a constant electric current between the cathode electrodes 88 and the anode electrode 98. In particular, at the initial stage, a low constant current ii, for example at about 1 to 10 mA/cm², preferably at about 3 to 7 mA/cm², is applied so as to gradually grow a plated film (t₁-t₂). When the thickness of the plated film has reached a predetermined value, for example about 0.05 to 0.5 μm, preferably about 0.1 to 0.2 μm, a high constant current i₂ (i₂>i₁), for example at about 10 to 40 mA/cm², preferably at about 25 mA/cm², is applied so as to rapidly grow the plated film, thereby effecting embedding of copper. During the plating, the substrate holder 36 is rotated at a low speed, according to necessity.

[0088] The seed layer 8, which can be prevented from being dissolved with the plating solution as described above, is thus reinforced in the first-step plating carried out with a low electric current, and the plated film is allowed to grow in the second-step plating whereby embedding of copper is effected. Such a two-step plating can form defect-free, completely-embedded interconnects of a conductive material, such as copper, in recesses in the surface of a substrate even when the recesses are of a high aspect ratio.

[0089] When the plating process is completed, the electrode arm portion 30 is raised and then swung to return to the position above the plating solution tray 22 and to lower to the ordinary position. Then, the pre-coating/recovering arm 32 is moved from the retreat position to the position confronting to the substrate W, and lowered to recover the remainder of the plating solution on the substrate W by a plating solution recovering nozzle 66. After recovering of the remainder of the plating solution is completed, the pre-coating/recovering arm 32 is returned to the retreat position, and pure water is supplied from the fixed nozzle 34 for supplying pure water toward the central portion of the substrate W for rinsing the plated surface of the substrate. At the same time, the substrate holder 36 is rotated at an increased speed to replace the plating solution on the surface of the substrate W with pure water. Rinsing the substrate W in this manner prevents the splashing plating solution from contaminating the cathode electrodes 88 of the electrode portion 38 during descent of the substrate holder 36 from the plating position B.

[0090] After completion of the rinsing, the washing with water step is initiated. That is, the substrate holder 36 is lowered from the plating position B to the pretreatment/cleaning position C. Then, while pure water is supplied from the fixed nozzle 34 for supplying pure water, the substrate holder 36 and the electrode portion 38 are rotated to perform washing with water. At this time, the sealing member 90 and the cathode electrodes 88 can also be cleaned, simultaneously with the substrate W, by pure water directly supplied to the electrode potion 38, or pure water scattered from the surface of the substrate W.

[0091] After washing with water is completed, the drying step is initiated. That is, supply of pure water from the fixed nozzle 34 is stopped, and the rotational speed of the substrate holder 36 and the electrode portion 38 is further increased to remove pure water on the surface of the substrate W by centrifugal force and to dry the surface of the substrate W. The sealing member 90 and the cathode electrodes 88 are also dried at the same time. Upon completion of the drying, the rotation of the substrate holder 36 and the electrode portion 38 is stopped, and the substrate holder 36 is lowered to the substrate transfer position A. Thus, the gripping of the substrate W by the chucking fingers 76 is released, and the substrate W is just placed on the upper surfaces of the support arms 70. At the same time, the cup 40 is also lowered.

[0092] All the steps including the plating step, the pretreatment step accompanying to the plating step, the cleaning step, and the drying step are now finished. The transfer robot 14 inserts its hand through the substrate carry-in and carry-out opening into the position beneath the substrate W, and raises the hand to receive the plated substrate W from the substrate holder 36. Then, the transfer robot 14 returns the plated substrate W received from the substrate holder 36 to one of the loading/unloading units 10.

[0093]FIG. 13 shows another control method (plating method) as carried out by the plating apparatus. According to this method, the negative pole of the plating power source 114 is connected to the cathode electrodes 88 and the positive pole is connected to the anode electrode 98, and a voltage (e.g. constant voltage) is applied between the cathode electrodes 88 and the anode electrode 98, while a plating solution is supplied from the plating solution supply pipe 102 into the electrode head 28, so that the plating solution is supplied onto the upper surface (plating surface) of the substrate W while the high resistance structure 110 is impregnated with the plating solution and the plating solution chamber 100 is filled with the plating solution (t₀-t₄).

[0094] After completion of the filling of plating solution, a plated film is allowed to grow on the surface of the substrate W while carrying out constant current control, i.e., applying a constant electric current between the cathode electrodes 88 and the anode electrode 98. In particular, at the initial stage, a low constant current i₃, for example at about 1 to 10 mA/cm², preferably at about 3 to 7 mA/cm², is applied so as to gradually grow a plated film (t₄-t₅). When the thickness of the plated film has reached a predetermined value, for example about 0.05 to 0.5 μm, preferably about 0.1 to 0.2 μm, the electric current (voltage) is switched so that the cathode electrodes 88 becomes an anode and the anode electrode 98 becomes a cathode, and a constant current (−i₄) is applied between the cathode electrodes 88 and the anode electrode 98 so as to etch away the surface of the plated film and flatten the plated film (t₅-t₆). Thereafter, the electric current (voltage) is switched so that the cathode electrodes 88 becomes a cathode and the anode electrode 98 becomes an anode, and a high constant current i₅ (i₅>i₃), for example at about 10 to 40 mA/cm², preferably at about 25 mA/cm², is applied so as to rapidly grow the plated film, thereby effecting embedding of copper.

[0095] By thus etching away the surface of a plated film between the plating steps to flatten the plated film, the flatness of the final plated film can be improved. In this connection, when a barrier layer 6 is formed on the surface of a substrate W in which relative small and large fine recesses, e.g. narrow trenches 5 a and broad trenches 5 b, are co-present in the surface, as shown in FIG. 17A, and a seed layer 8 is formed on the barrier layer 6, and then copper plating is carried out to grow a plated film to effect embedding of copper film 7, the growth of plating tends to be promoted over the narrow trenches 5 a whereby the copper film 7 is likely to be raised, even when the seed layer 8 can be prevented from being dissolved with the plating solution as described above. According to the present method, the raised portions 7 a of the plated copper film 7, shown by the broken line in FIG. 17B, are etched away and a plated film is further grown on the flattened copper film 7 b to finally form a copper film 7 c. The flatness of the plated film (copper film 7) can thus be improved.

[0096]FIG. 14 shows yet another method (plating method) as carried out by the plating apparatus. According to this method, the negative pole of the plating power source 114 is connected to the cathode electrodes 88 and the anode electrode 98, i.e. constant voltage control is carried out, while a plating solution is supplied from the plating solution supply pipe 102 into the electrode head 28, so that the plating solution is supplied onto the upper surface (plating surface) of the substrate W while the high resistance structure 110 is impregnated with the plating solution and the plating solution chamber 100 is filled with the plating solution (t₀-t₈).

[0097] After completion of the filling of plating solution, a plated film is allowed to grow on the surface (seed layer 8) of the substrate while carrying out constant current control, i.e., applying a constant electric current between the cathode electrodes 88 and the anode electrode 98. In particular, at the initial stage, a low constant current i₆, which is lower than the electric current applied between the cathode electrodes 88 and the anode electrode 98 upon the constant voltage control, for example at about 1 to 10 mA/cm², preferably at about 3 to 7 mA/cm², is applied so as to gradually grow a plated film (t₈-t₉). When the thickness of the plated film has reached a predetermined value, for example about 0.05 to 0.5 μm, preferably about 0.1 to 0.2 μm, a high constant current i₆ (i₆>i₅), for example at about 10 to 40/cm², preferably at about 25 mA/cm², is applied so as to rapidly grow the plated film, thereby effecting embedding of copper. During the plating, the substrate holder 36 is rotated at a low speed, according to necessity.

[0098]FIG. 15 shows yet another control method (plating method) as carried out by the plating apparatus. According to this method, the negative pole of the plating power source 114 is connected to the cathode electrodes 88 and the positive pole is connected to the anode electrode 98, and a constant voltage is applied between the cathode electrodes 88 and the anode electrode 98, i.e. constant voltage control is carried out, while a plating solution is supplied from the plating solution supply pipe 102 into the electrode head 28, so that the plating solution is supplied onto the upper surface (plating surface) of the substrate W while the high resistance structure 110 is impregnated with the plating solution and the plating solution chamber 100 is filled with the plating solution (t₀-t₁₁).

[0099] After completion of the filling of plating solution, a plated film is allowed to grow on the surface (seed layer 8) of the substrate while carrying out constant current control, i.e., applying a constant electric current between the cathode electrodes 88 and the anode electrode 98. In particular, at the initial stage, a low constant current i₈, which is higher than the electric current applied between the cathode electrodes 88 and the anode electrode 98 upon the constant voltage control, for example at about 1 to 10 mA/cm², preferably at about 3 to 7 mA/cm², is applied so as to gradually grow a plated film (t₁₁-t₁₂). When the thickness of the plated film has reached a predetermined value, for example about 0.05 to 0.5 μm, preferably about 0.1 to 0.2 μm, a high constant current i₉ (i₉>i₈), for example at about 10 to 40 mA/cm², preferably at about 25 mA/cm², is applied so as to rapidly grow the plated film, thereby effecting embedding of copper. During the plating, the substrate holder 36 is rotated at a low speed, according to necessity.

[0100]FIG. 16 shows yet another control method (plating method) as carried out by the plating apparatus. This method effects embedding of copper by using two plating solutions of different compositions. In particular, the negative pole of the plating power source 114 is connected to the cathode electrodes 88 and the positive pole is connected to the anode electrode 98, and a constant voltage is applied between the cathode electrodes 88 and the anode electrode 98, i.e. constant voltage control is carried out, while a plating solution is supplied from the plating solution supply pipe 102 into the electrode head 28, so that the plating solution is supplied onto the upper surface (plating surface) of the substrate W while the high resistance structure 110 is impregnated with the plating solution and the plating solution chamber 100 is filled with the plating solution (t₀-t₁₄).

[0101] After completion of the filling of plating solution, a plated film is allowed to grow on the surface (seed layer 8) of the substrate while carrying out constant current control, i.e., applying a constant electric current between the cathode electrodes 88 and the anode electrode 98. In particular, at the initial stage, a low constant current i₁₀, for example at about 3 to 7 mA/cm², is applied so as to gradually grow a plated film (t₁₄-t₁₅).

[0102] In the initial stage of plating, a plating solution suited for embedding of fine (narrow) patterns is employed. The following is an example of the composition of such plating solution: CuSO₄.5H₂O 200 g/l H₂SO₄ 50 g/l HCl 60 mg/l Organic additive 5 ml/l

[0103] When the thickness of the plated film has reached a predetermined value, for example about 0.05 to 0.5 μm, preferably about 0.1 to 0.2 μm, the plating operation is stopped, and the plating solution is removed and the surface of the plated film is cleaned e.g. with pure water in the above-described manner.

[0104] Next, a high constant current ill (i₁₁>i₁₀), for example at about 20 to 40 mA/cm², preferably at about 25 MA/cm², is applied so as to rapidly grow the plated film, thereby effecting embedding of copper.

[0105] In the latter stage of plating, a plating solution suited for embedding of broad patterns, e.g. containing 100 to 300 g/l of copper sulfate and 10 to 10 g/l of sulfuric acid, is employed. The following is an example of the composition of such plating solution: CuSO₄.5H₂O 200 g/l H₂SO₄ 50 g/l HCl 100 mg/l Organic additive 5 ml/l

[0106]FIG. 18 shows another plating apparatus useful for carrying out the plating method of the present invention. The plating apparatus includes an upwardly-open cylindrical plating tank 602 for holding a plating solution 600, and a rotatable substrate holder 604 for detachably holding a substrate W, such as a semiconductor wafer, with its front surface facing downward and locating the substrate W at a position at which it closes the top opening of the plating tank 602. An anode electrode 606 in a flat plate shape which, when immersed in the plating solution 600, serves as an anode is disposed horizontally in the plating tank 602. A seed layer, formed in the surface of the substrate W, serves as a cathode. The anode electrode 606 may be comprised of, for example, a plate of copper or an aggregate of copper balls.

[0107] A plating solution supply pipe 610, which is provided with a pump 608 therein, is connected to the center of the bottom of the plating tank 602. Further, a plating solution receiver 612 is disposed around the plating tank 602. The plating solution that has flowed into the plating solution receiver 612 is returned through a plating solution return pipe 614 to the pump 608.

[0108] In operation, the substrate W, held face down by the substrate holder 604 and located at an upper position in the plating tank 602, is rotated and a predetermined voltage is applied between the anode electrode 606 and the seed layer (cathode electrode) of the substrate W while the pump 608 is driven to introduce the plating solution 600 into the plating tank 602, whereby a plating current is allowed to flow between the anode electrode 606 and the seed layer of the substrate W, and a plated copper film is formed on the lower surface of the substrate W. During the plating, the plating solution 600 overflowing the plating tank 602 is recovered by the plating solution receiver 612 and circulated.

[0109] An insulator 632 in a flat plate shape is disposed between the anode electrode 606 immersed in the plating solution 600 in the plating tank 602 and the substrate W held by the substrate holder 604 and located at an upper position in the plating tank 602. A plurality of through-holes 632 b of any desired sizes (diameters) are provided at any desired locations in the insulator 632 so that a plating current can flow only through the through-holes 632 b, making it possible to make a plated copper film thicker at desired portions of the substrate.

[0110] Also with the plating apparatus of such a construction, by carrying out the same control as described above, it becomes possible to form defect-free, completely-embedded interconnects of a conductive material in recesses in the surface of a substrate even when the recesses are of a high aspect ratio, and improve the flatness of a plated film on the substrate even when narrow trenches and broad trenches are co-present in the surface of the substrate, enabling a later CMP processing to be carried out in a short time while preventing dishing during the CMP processing.

[0111]FIG. 19 shows an overall layout plan of another substrate processing apparatus provided with a plating apparatus for carrying out a plating method according to the present invention. The substrate processing apparatus (interconnects-forming apparatus) includes two loading/unloading sections 202 for carrying a substrate in and out a main frame 200. Inside the main frame 200 are disposed a heat treatment apparatus 204 for heat-treating (annealing) a plated film formed on the substrate, a bevel-etching apparatus 206 for removing a plated film formed on or adhering to a peripheral portion of the substrate, two cleaning/drying apparatuses 208 for cleaning the surface of the substrate with a cleaning liquid, such as a chemical liquid or pure water, and spin-drying the cleaned substrate, a substrate stage 210 for temporarily placing the substrate thereon, and two plating apparatuses 212. Inside the main frame 200 are also provided a movable first transfer robot 214 for transferring the substrate between the loading/unloading sections 202 and the substrate stage 210, and a movable second transfer robot 216 for transferring the substrate between the substrate stage 210, the heat treatment apparatus 204, the bevel-etching apparatus 206, the cleaning/drying apparatuses 208 and the plating apparatuses 212. According to this embodiment, the plating apparatus 212 has a similar construction to that of the plating apparatus 12 shown in FIGS. 1 through 11.

[0112] The main frame 200 has been made light-shielding so that the following process steps can be carried out under light-shielded conditions in the main frame 200, i.e. without irradiation of a light, such as an illuminating light, onto the interconnects of the substrate. This prevents corrosion of the interconnects of e.g. copper due to potential difference that would be produced by light irradiation onto the interconnects.

[0113] Positioned beside the main frame 200, there is provided a plating solution control apparatus 224 which includes a plating solution tank 220 and a plating solution analyzer 222, and which analyzes and controls the components of a plating solution for use in the plating apparatuses 212 and supplies the plating solution of a predetermined composition to the plating apparatuses 212. The plating solution analyzer 222 includes an organic material analysis section for analyzing an organic material by cyclic voltammetry (CVS), liquid chromatography, etc., and an inorganic material analysis section for analyzing an inorganic material by neutralization titration, oxidation-reduction titration, polarography, electrometric titration, etc. The results of analysis by the plating solution analyzer 222 are fed back to adjust the components of the plating solution in the plating solution tank 220. The plating solution control apparatus 224 may also be disposed inside the main frame 200.

[0114] An example of the formation of copper interconnects by the substrate processing apparatus, as illustrated in FIG. 20, will now be described.

[0115] First, substrates W having a seed layer 8 (see FIG. 17B) as an electric feeding layer formed on the surface are prepared, and a substrate cassette housing the substrates is mounted in the loading/unloading section 202. One substrate W is taken by the first transfer robot 214 out of the cassette mounted in the loading/unloading section 202, and the substrate is carried in the main frame 200, transferred to the substrate stage 210, and placed and held on the substrate stage 210. The substrate held on the substrate stage 210 is transferred by the second transfer robot 216 to one of the plating apparatuses 212.

[0116] In the plating apparatus 212, as with the above-described embodiment, a pre-plating treatment, such as pre-coating, of the surface (plating surface) of the substrate W is first carried out. Thereafter, plating of the substrate is carried out under a current/voltage control as shown in FIG. 13, for example. Thus, a plated copper film is first grown gradually on the surface of the substrate W, the surface of the plated copper film is then etched away to flatten the plated copper film, and the plated copper film is then grown rapidly to effect embedding of copper. During the processing, the composition of the plating solution in the plating solution tank 220 is analyzed by the plating solution analyzer 222, and a shortage of a component is replenished in the plating solution in the plating solution tank 220 so that the plating solution of a constant composition is supplied to the plating apparatus 212. After completion of the plating, as with the above-described embodiment, the plating solution remaining on the substrate is recovered and the plated surface of the substrate is rinsed, and the surface of the substrate is cleaned (water-washed) with e.g. pure water. The substrate after cleaning is transferred by the second transfer robot 216 to the bevel-etching apparatus 206.

[0117] In the bevel-etching apparatus 206, while rotating the substrate which is held horizontally, an acid solution is supplied continuously to the central portion of the front surface of the substrate and an oxidant solution is supplied continuously or intermittently to a peripheral portion of the front surface. The acid solution may be of any non-oxidative acid, such as hydrofluoric acid, hydrochloric acid, sulfuric acid, citric acid, oxalic acid, etc. Examples of the oxidant solution include ozone water, hydrogen peroxide solution, nitric acid solution, and sodium hypochlorite solution, and a combination thereof. Copper, etc. formed on or adhering to a peripheral portion (bevel portion) of the substrate W is rapidly oxidized by the oxidant solution, and the oxidized product is etched and dissolved out by the acid solution which is supplied to the central portion of the substrate and spreads over the entire surface of the substrate.

[0118] During the above etching processing, an oxidant solution and an etching agent for silicon oxide film may be supplied simultaneously or alternately to the central portion of the back surface of the substrate, thereby oxidizing copper etc. in elemental form adhering to the back surface of the substrate W, together with the silicon of the substrate, with the oxidant solution and etching away the oxidized product with the etching agent.

[0119] The substrate after bevel-etching is transferred by the second transfer robot 216 to one of the cleaning/drying apparatuses 208, where the surface of the substrate is cleaned with a cleaning liquid, such as a chemical liquid or pure water, followed by spin-drying. The dried substrate is transferred by the second transfer robot 216 to the heat treatment apparatus 204.

[0120] In the heat treatment apparatus 204, heat treatment (annealing) of the copper film 7 (see FIG. 21B) formed on the surface of the substrate W is carried out, thereby crystallizing the copper film 7 forming interconnects. The heat treatment (annealing) is carried out by heating the substrate, for example, at 400° C. for about a few tens of seconds to 60 seconds. At the same time, if necessary, a gas for oxidation inhibition is introduced into the heat treatment apparatus 204 and is allowed to flow along the surface of the substrate to prevent oxidation of the surface of the copper film 7. The heating temperature of the substrate is generally 100 to 600° C., preferably 300 to 400° C.

[0121] The substrate W after heat treatment is transferred by the second transfer robot 216 to the substrate stage 210 and held on the substrate stage 210. The substrate on the substrate stage 210 is transferred by the first transfer robot 214 to the cassette of the loading/unloading section 202.

[0122] Thereafter, extra metal formed on the insulating film and the barrier layer are removed by method such as chemical mechanical polishing (CMP) so as to flatten the surface, whereby forming interconnects composed of the copper film 7, as shown in FIG. 21C.

[0123] Though in this embodiment copper is used as an interconnect metal, it is possible to use a copper alloy instead.

[0124] The following Examples illustrate copper plating of the surface of a substrate by a plating method according to the present invention.

[0125] In each of the Examples, two types of substrates are used: silicon wafer (diameter: 200 mm) with holes having a hole diameter of 0.15-0.50 μm and a depth of 0.8 μm; and silicon wafer (diameter: 200 mm) with trenches having a width of 0.12-1.0 μm. Seed layers are formed on the surfaces of these substrates by PVD to make electrical conduction, followed by copper plating using a copper sulfate plating solution.

EXAMPLE 1

[0126] A copper sulfate plating solution having the following composition was used: Copper sulfate pentahydrate: 200 g/L Sulfuric acid: 50 g/L Chlorine: 60 mg/L Additive: Proper amount

[0127] Ebatoronfil (manufactured by Ebara-Udylite Co., Ltd) was used as the additive.

[0128] For each of the above-described substrates, electroplating was carried out in the following manner:

[0129] A voltage of 0.4V had been applied in advance to the substrate (the current density at the substrate surface upon contact of the substrate with the plating solution was 7 mA/cm²), and the plating solution was filled into the space between the substrate and an anode electrode. The application of the constant voltage was continued for 500 msec after the filling of the plating solution. Thereafter, the constant voltage control was instantaneously changed to constant current control and a constant current was applied at 7 mA/cm² for 30 sec to form a copper film, and then a constant current was applied at 25 mA/cM² for 50 sec to further grow the plated film, thereby depositing a copper film having a thickness, on the plane of the substrate, of about 500 nm.

EXAMPLE 2

[0130] The same substrates and the same plating solution as in Example 1 were used. For each of the substrates, electroplating was carried out in the following manner:

[0131] A voltage of 1.0V had been applied in advance to the substrate (the current density at the substrate surface upon contact of the substrate with the plating solution was 20 mA/cm²), and the plating solution was filled into the space between the substrate and an anode electrode. The application of the constant voltage was continued for 300 msec after the filling of the plating solution. Thereafter, the constant voltage control was instantaneously changed to constant current control and a constant current was applied at 10 mA/cm² for 30 sec to form a copper film, and then a constant current was applied at 20 mA/cm² for 53 sec to further grow the plated film, thereby depositing a copper film having a thickness, on the plane of the substrate, of about 500 nm.

EXAMPLE 3

[0132] The same substrates and the same plating solution as in Example 1 were used. For each of the substrates, electroplating was carried out in the following manner:

[0133] A voltage of 0.7V had been applied in advance to the substrate (the current density at the substrate surface upon contact of the substrate with the plating solution was 15 mA/cm²), and the plating solution was filled into the space between the substrate and an anode electrode. The application of the constant voltage was continued for 500 msec after the filling of the plating solution. Thereafter, the constant voltage control was instantaneously changed to constant current control and a constant current was applied at 7 mA/cm² for 40 sec to form a copper film, and then reverse electrolysis was carried out at 20 mA/cm² for 4 sec, and then a constant current was applied at 25 mA/cm² for 52 sec to further grow the plated film, thereby depositing a copper film having a thickness, on the plane of the substrate, of about 500 nm.

COMPARATIVE EXAMPLE 1

[0134] The same substrates and the same plating solution as in Example 1 were used. For each of the substrates, electroplating was carried out in the following manner:

[0135] The plating solution was filled into the space between the substrate and an anode electrode without application of a voltage therebetween. 500 msec after the filling of the plating solution, a constant current was applied at 7 mA/cm² for 30 sec to form a copper film, and then a constant current was applied at 25 mA/cm² for 50 sec to further grow the plated film, thereby depositing a copper film having a thickness, on the plane of the substrate, of about 500 nm.

[0136] A hole portion or a trench portion of each of the substrates with the plated copper film, obtained in the above Examples 1 to 3 and Comp. Example 1, was cut off by means of FIB (focused in beam) and the cut surface was observed by SEM (scanning electron micrograph). As a result, with respect to the substrates of Examples 1 to 3, no void was observed in the substrates having fine holes or in the substrates having fine trenches. In contrast thereto the substrates of Comp. Example 1, many voids were observed at the bottom portions of fine holes and trenches.

[0137] As described hereinabove, the present invention makes it possible to form defect-free, completely-embedded interconnects of a conductive material in recesses in the surface of a substrate even when the recesses are of a high aspect ratio, and improve the flatness of a plated film on the substrate even when narrow trenches and broad trenches are co-present in the surface of the substrate, enabling a later CMP processing to be carried out in a short time while preventing dishing during the CMP processing.

[0138] Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims. 

What is claimed is:
 1. A plating method, comprising: providing a high resistance structure between a surface of a substrate, said surface being connected to a cathode electrode, and an anode electrode; filling the space between the substrate and the anode electrode with a plating solution while applying a voltage between the cathode electrode and the anode electrode; and growing a plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at a constant value.
 2. The plating method according to claim 1, wherein the voltage is applied for 100 to 2000 msec after the electric current begins to flow between the cathode electrode and the anode electrode.
 3. The plating method according to claim 1, wherein the voltage applied is such as to allow an electric current with an average cathodic current density, with respect to the surface of the substrate, of 1 to 30 mA/cm² to flow.
 4. The plating method according to claim 3, wherein the voltage is applied for 100 to 2000 msec after the electric current begins to flow between the cathode electrode and the anode electrode.
 5. A plating method, comprising: providing a high resistance structure between a surface of a substrate, said surface being connected to a cathode electrode, and an anode electrode; filling the space between the substrate and the anode electrode with a plating solution; and growing a plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at stepwise changing constant values.
 6. The plating method according to claim 5, wherein the plating solution is changed for a different plating solution in the process of film formation.
 7. The plating method according to claim 6, wherein the surface of the substrate is cleaned in the process of film formation.
 8. The plating method according to claim 5, wherein the value of the electric current flowing between the cathode electrode and the anode electrode is increased stepwise.
 9. The plating method according to claim 8, wherein the plating solution is changed for a different plating solution in the process of film formation.
 10. The plating method according to claim 9, wherein the surface of the substrate is cleaned in the process of film formation.
 11. A plating method, comprising: providing a high resistance structure between a surface of a substrate, said surface being connected to a cathode electrode, and a anode electrode; filling the space between the substrate and the anode electrode with a plating solution; growing a plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at a constant value; reversing the direction of the electric current flowing between the cathode electrode and the anode electrode to etch away the surface of the plated film; and further growing the plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at a constant value.
 12. The plating method according to claim 11, wherein the step of etching the surface of the plated film and the subsequent step of growing the plated film are carried out repeatedly.
 13. A plating method, comprising: filling the space between a surface of a substrate, said surface being connected to a cathode electrode, and an anode electrode with a plating solution while applying a voltage between the cathode electrode and the anode electrode; and growing a plated film on the surface of the substrate while controlling an electric current flowing between the cathode electrode and the anode electrode at a constant value.
 14. The plating method according to claim 13, wherein the voltage is applied for 100 to 200 msec after the electric current begins to flow between the cathode electrode and the anode electrode.
 15. The plating method according to claim 13, wherein the voltage applied is such as to allow an electric current with an average cathodic current density, with respect to the surface of the substrate, of 1 to 30 mA/cm² to flow.
 16. The plating method according to claim 15, wherein the voltage is applied for 100 to 2000 msec after the electric current begins to flow between the cathode electrode and the anode electrode. 